Still from American Sniper. The comic is never named, but if you look closely, you can see that it's issue No. 1 of the sixth volume of Punisher, released in January of 2004 (making it very believable as something Biggles could be reading during the platoon's 2004 deployment).
A Dr. Garry Choy, MD, Diagnostic Radiology, answered. Radiation fibrosis is the result of prior radiation exposure that results in scarring of an organ such as breasts, lungs, etc. Post radiation treatment fibrosis is the typical cause.
Exposure to high levels of radon through breathing air is known to cause lung diseases. When long-term exposure occurs radon increases the chances of developing lung cancer. Radon can only cause cancer after several years of exposure. Radon may be radioactive, but it gives of little actual gamma radiation. As a result, harmful effects from exposure to radon radiation without actual contact with radon compounds are not likely to occur. It is not known whether radon can cause health effects in other organs besides the lungs. The effects of radon, which is found in food or drinking water, are unknown.